1. Field of the Invention
The present invention relates to a drive wheel bearing device for rotatably supporting a drive wheel (the front wheels of a front wheel drive vehicle, the rear wheels of a rear wheel drive vehicle, and all the wheels of a four wheel drive vehicle) with respect to the suspension of the vehicle.
2. Description of the Related Art
Vehicle wheel bearing devices are used for driven wheels and drive wheels. Various types of bearing devices have been suggested according to their respective applications. For example, FIG. 3 shows a drive wheel bearing device which mainly includes a wheel hub 1, an inner ring 2, double rows of rollers 3 and 4, an outer ring 5, and a constant velocity universal joint 6.
The wheel hub 1 has an outboard race surface 7 formed on its outer circumference surface and a wheel mounting flange 9 for mounting a wheel (not shown). The wheel mounting flange 9 has hub bolts 10 embedded at equal intervals along the circumference thereof to secure a wheel disc. There is also provided a reduced diameter step portion 12 on the outer circumference surface of the wheel hub 1. The inner ring 2 is fitted over the reduced diameter step portion 12, and an inboard race surface 8 is formed on the outer circumference surface of the inner ring 2.
The inner ring 2 is fitted to have an appropriate crimp margin to prevent creep. The outboard race surface 7 formed on the outer circumference surface of the wheel hub 1 and the inboard race surface 8 formed on the outer circumference surface of the inner ring 2 constitute double rows of race surfaces. The inner ring 2 is fitted over the reduced diameter step portion 12 of the wheel hub 1, and then the end portion of the reduced diameter step portion 12 of the wheel hub 1 is swaged outwardly. This causes a swaged portion 11 to prevent the inner ring 2 from dislodging, thereby allowing the inner ring 2 to be integrated with the wheel hub 1 and provide preload to a bearing portion 20.
The outer ring 5 is provided, on its inner circumference surface, with double rows of race surfaces 13 and 14 formed to oppose the race surfaces 7 and 8 of the wheel hub 1 and the inner ring 2. The outer ring 5 also has a vehicle body mounting flange 17 for mounting it to the vehicle body (not shown). The vehicle body mounting flange 17 is securely bolted to a knuckle joint extending from the suspension (not shown) of the vehicle body using a mount hole 19.
The bearing portion 20 includes a double row angular contact ball bearing, in which the rollers 3 and 4 are interposed between the race surfaces 7 and 8 formed on the outer circumference surfaces of the wheel hub 1 and the inner ring 2 and the race surfaces 13 and 14 formed on the inner circumference surface of the outer ring 5. In this arrangement, each row of the rollers 3 and 4 is held at equal intervals along the circumference by the respective retainers 21 and 22. At both the openings of the bearing portion 20, a pair of seals 23 and 24 is fitted into the inner diameter at the respective ends of the outer ring 5 so as to slidingly contact with the outer circumference surfaces of the wheel hub 1 and the inner ring 2. The seals 23 and 24 are provided to seal the respective annular spaces between the outer ring 5 and the wheel hub 1 and between the outer ring 5 and the inner ring 2, thereby preventing leakage of grease filled in the bearing portion 20 and intrusion of external moisture or foreign matters.
The constant velocity universal joint 6 is provided at one end of an intermediary shaft (not shown) which is part of a driveshaft. The joint 6 includes: a joint outer ring 15 having a track groove formed on its inner circumference surface; a joint inner ring (not shown) having a track groove formed on its outer circumference surface so as to oppose the track groove of the joint outer ring 15; and balls (not shown) incorporated between the track groove of the joint outer ring 15 and the track groove of the joint inner ring. The joint outer ring 15 includes a mouse portion 25 for receiving the joint inner ring and the balls, and a stem portion 27 which axially extends integrally from the mouse portion 25 and which has a serrated portion 26 on its outer circumference surface.
The stem portion 27 is inserted into a through hole of the wheel hub 1 to allow a shoulder portion 16 of the joint outer ring 15 to abut the swaged portion 11 of the wheel hub 1. Under this condition, a nut 30 is firmly screwed down on a male screw portion 29 formed on the end portion of the stem portion 27, thereby securing the constant velocity universal joint 6 to the wheel hub 1. The engagement of the serrated portion 26 formed on the outer circumference surface of the stem portion 27 with a serrated portion 28 formed on the inner circumference surface of the through hole allows for torque transmission.
The drive wheel bearing device may possibly generate a click-clack squeak noise or a so-called stick slip noise, e.g., when the vehicle starts to move, between the swaged portion 11 of the wheel hub 1 of the bearing portion 20 and the shoulder portion 16 of the joint outer ring 15 of the constant velocity universal joint 6.
At the time of the vehicle starting to move, this stick slip noise may be generated when rotational torque is loaded from the joint outer ring 15 of the constant velocity universal joint 6 to the wheel hub 1 of the bearing portion 20, which is stationary. More specifically, the rotational torque is transferred from the joint outer ring 15 to the wheel hub 1 via the serrated portions 26 and 28, and thus a twist of the joint outer ring 15 causes the shoulder portion 16 of the joint outer ring 15 to abruptly slide past the swaged portion 11 of the wheel hub 1. This sudden sliding results in the stick slip noise.
Several means for preventing the stick slip noise have been suggested. For example, one means is disclosed in Japanese Patent Laid-Open Publication No. 2003-97588 or 2003-118309, in which the end face of the shoulder portion 16 of the joint outer ring 15 is provided with bumps and dips or blasted by shot peening to provide an increased frictional resistance to the abutted portion between the swaged portion 11 of the wheel hub 1 and the shoulder portion 16 of the joint outer ring 15. Another means is also disclosed, e.g., in Japanese Patent Laid-Open Publication No. 2003-136908, in which the flat end face of the swaged portion 11 of the wheel hub 1 is provided with recessed grooves in which grease is filled, thereby providing a reduced frictional resistance to the abutted portion between the swaged portion 11 of the wheel hub 1 and the shoulder portion 16 of the joint outer ring 15.
The wheel bearing device of the type currently in vogue is configured such that the swaged portion 11 of the wheel hub 1 abuts the shoulder portion 16 of the joint outer ring 15. The aforementioned means are adapted to prevent the stick slip noise by providing an increased or conversely reduced frictional resistance to the abutted portion between the swaged portion 11 of the wheel hub 1 and the shoulder portion 16 of the joint outer ring 15. However, the applicant has experimentally found that for the current type of the wheel bearing device, the aforementioned means are not sufficiently enough to prevent the stick slip noise.